This invention generally relates to medical devices, and particularly balloon molds for making balloons for intravascular balloon catheters.
In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced in the patient's vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. A dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with inflation fluid one or more times to a predetermined size at relatively high pressures so that the stenosis is compressed against the arterial wall and the wall expanded to open up the vascular passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter and the guidewire can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate of angioplasty alone and to strengthen the dilated area, physicians now normally implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel or to maintain its patency. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded within the patient's artery to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference.
Catheter balloons are typically formed by a blow molding process, in which a polymeric tube is heated and expanded in a mold. The mold has an interior chamber corresponding to the desired configuration of the inflated balloon. The resulting blow molded balloon typically inflates to form an inflated working length, inflated tapering sections on either end of the working section, and proximal and distal skirt sections configured to be attached to the catheter shaft, although conventional balloons may have a variety of configurations depending on the desired use of the balloon catheter. A balloon having a disadvantageously large wall thickness will increase the profile and stiffness of the distal end of the catheter, thus decreasing the maneuverability and crossability (i.e., the ability of the catheter to be positioned across the lesion to be dilated) of the catheter. While considerable development effort has been directed at producing catheter balloons having thinned taper and shaft sections, none of the methods heretofore developed have been completely satisfactory. Prior methods involving removal of balloon material after the balloon is blow molded complicate manufacture of the balloon, and may damage the balloon. Precisely and accurately thinning a section of the balloon to a desired wall thickness has proven difficult. For example, one difficulty has been providing balloon tapered sections having a specific small wall thickness. Thus, it would be a significant advance to provide a catheter balloon and method of making the balloon, having walls with a desired thin wall thickness.